EP0985810A1 - Method and device for minimizing thermo-acoustic oscillations in gas turbine combustion chambers - Google Patents

Abstract

The process involves modulating the injection of liquid or gaseous pre-mixed fuel. An Independent claim is included for a device for controlling themoacoustic oscillation in a combustion system comprising a burner having two fuel pipes with openings to the injection of the fuel. The system further comprises several sensors and a device for modulating the injection of the pre mixed fuel with respect to the measured signal of the sensors.

Description

Technical field

The invention relates to a method and an apparatus for Minimize thermoacoustic vibrations in Gas turbine combustors.

State of the art

It is known that undesired thermoacoustic vibrations often occur in combustion chambers of gas turbines. The term "thermoacoustic vibrations" denotes mutually rocking thermal and acoustic disturbances. High vibration amplitudes can occur, which can lead to undesired effects, such as a high mechanical load on the combustion chamber, an increased NO _x emission due to inhomogeneous combustion and even an extinguishing of the flame. This is particularly true for combustion systems with low acoustic damping. In order to guarantee high performance in terms of pulsations and emissions over a wide operating range, active control of the combustion vibrations may be necessary.

The fluid mechanical stability of a gas turbine burner is vital to the appearance thermoacoustic vibrations. The arising in the burner Fluid-mechanical instability waves lead to training of eddies. These are also referred to as coherent structures Eddies play an important role in mixing processes between air and fuel. The dynamic of the coherent Structures affect combustion and the associated Heat release. The vertebrae can therefore become periodic Heat release of the burner flame and thus too Pressure fluctuations. Especially if over the entire Area of the burner no homogeneous mixing of fuel and air is given, the emergence of coherent affects Vortex structures rely heavily on the formation of thermoacoustic Instabilities. So there is another possibility Reduction of the tendency of a burner to vibrate in the Stabilization of the flame of the premix burner.

Presentation of the invention

This is where the invention comes in. It is supposed to be a procedure for Minimize the pressure amplitude of thermoacoustic vibrations in Gas turbine combustors are created. This task will according to the invention by the method for minimizing the Pressure amplitude of thermoacoustic vibrations in one Gas turbine of independent claim 1, and by the Device solved according to independent claim 13.

The amount of fuel that is implemented in large-scale eddies controlled modulation of the fuel flow the premixing of a premix burner. According to the invention, liquid or gaseous fuel modulated in the premix burner. Under According to the invention, every modulated injection is temporal understood varying injection of fuel. The modulation can take place according to the invention with any frequency. The injection is preferably carried out at a frequency between 0.3 Hz and 5 kHz, with the range from 5 Hz to 200 Hz particularly is preferred. The injection takes place independently of the phase from the pressure vibrations in the combustion system.

Figure 1 shows a premix burner in which the Method according to the invention for minimizing the pressure amplitude thermoacoustic vibrations can be used. The Burner has two fuel lines 13, 14, which with Openings 15 are provided through which the gaseous or liquid fuel 16 is mixed with the combustion air 7.

The exact location of the openings 15 through which the fuel 16 is added to the combustion air 7 is clearer Figure 2 can be seen. The fuel lines 13, 14 are on the Partial bodies 1, 2 attached so that the openings 15 along two lines are lined up, parallel and in the same Distance from the main central axis 26 (= burner axis) of the Premix burner. All openings 15 are in one level, the fuel injection level.

According to the invention, fuel is injected through the Openings 15 are not constant in time, but modulated. It So the amount of fuel that is generated by the Fuel lines 13, 14 is supplied varies.

The fuel lines 13, 14 extend from a Calming chamber (not shown), which by a single Fuel line (not shown) is supplied towards the partial body 1, 2. According to this embodiment, the Modulation by opening and closing a fuel valve, which increases the amount of fuel that the calming chamber is supplied, and thus the amount of fuel that is transported through the fuel lines 13, 14, can be varied. According to this invention So embodiment is the amount of fuel in the two Fuel lines 13, 14 in the same way (symmetrical) varies.

According to a further embodiment of the invention, the amount supplied by a fuel line 13, 14 Fuel varies with the help of one fuel valve each. The burner described above must be technically modified become. This is done either by performing the Fuel lines 13, 14 through the calming chamber, whereby separate supply of fuel to the two lines is made possible, or by attaching one at a time separate calming chamber for each of the fuel lines 13, 14. These separate calming chambers are then separated fueled. In both cases the amount will increase Fuel that through the fuel lines 13, 14 the Premix burner is supplied with the help of one Fuel valve varies. The modulation by the Fuel line 13 supplied amount of fuel takes place thus regardless of the modulation by the Fuel line 14 supplied amount of fuel. Between Both modulated fuel flows can therefore be any There is a phase shift. In extreme cases, the Modulation of fuel flows out of phase by 180 ° (antisymmetric), i.e. at maximum injection by a There is minimal injection through the fuel line other fuel line.

The case of symmetrical modulation described above can of course also with the modified burner, i.e. with Helped by two fuel valves. In this corresponds to that of the one fuel valve permissible amount of fuel at any time in the essentially that of the second fuel valve amount of fuel passed.

Thus, according to the invention, any phase shift ϕ be used between the two fuel flows. According to In a preferred embodiment, the modulation takes place in both fuel lines uniform (ϕ = 0 °). According to one another, particularly preferred embodiment, the Modulation of fuel flows out of phase by 180 °, i.e. at maximum injection through a fuel line minimal injection through the other fuel line.

In the case of ϕ = 180 °, the is particularly effective Axial symmetry of the flame of the premix burner disturbed. As is known, in the case of low-frequency thermoacoustic Large amplitude pressure vibrations large-scale axially symmetrical Vortex structures for periodic heat release responsible. The effect of such structures on the The most effective way to influence combustion is by using the Axial symmetry of the flame is disturbed, which according to the present invention by the phase shift modulation of the two premix fuel flows is reached. Especially advantageous effects result for a phase shift of 180 °.

Alternatively, the injection within the scope of the present Invention according to a particularly preferred embodiment take place with the pressure fluctuations in a fixed Phase relationship. In this case, the phase of Pressure vibrations, for example, via a microphone in the Combustion chamber determined and this phase information for control the injection used.

The momentary injection of the fuel is preferred with a signal measured in the combustion system phase locked. Doing so will result in the combustion system Signal measured with the thermoacoustic vibrations is correlated. This signal can be downstream of the burner in the Combustion chamber or arranged upstream of the burner Calming chamber can be measured. It is then preferred Means are provided for the current injection of the fuel control as a function of the measurement signal.

By choosing a suitable one, depending on the type of measured Signals different phase difference between the measurement signal and the modulated injection of the Fuel in a particularly suitable way of training coherent structures, so that the amplitude of the Pressure pulsation is reduced.

A pressure signal in the combustion system is advantageous measured that with the thermoacoustic vibrations associated pressure fluctuations. This can be done with a or more in the combustion chamber, the calming chamber or on a wall of one of the chambers arranged microphones happen.

Another possibility is to measure an optical one Signal that with the heat release fluctuations of the Combustion process is correlated. It will be advantageous measured a chemiluminescence emission, preferably from one the radicals OH or CH. An optical signal is provided with a Sensor for visible or infrared radiation added, preferably an optical fiber probe.

The signal measured in the combustion system is advantageous filtered, phase-shifted and amplified, and the so obtained Signal as input signal for the control of the current Injection of liquid or gaseous fuel used. If necessary, the signal is also added before filtering reinforced. The filtering suppresses a disturbing noise signal and preferably consists of a bandpass filter. The Phase shift takes into account that usually through the Arrangement of the measuring sensors, by the measuring devices and the Lines even phase shifts occur. Will the relative phase chosen so that there is as large as possible Reduction in pressure amplitudes results in all of these phase-changing effects are implicitly taken into account. The value of Phase rotation can, after determining a favorable value, stay fixed. Since the cheapest relative phase is with operating conditions, the relative phase remains advantageously variable and is about a control of Pressure fluctuations tracked so that always a large one Suppression is guaranteed.

This phase-locked modulation of the premix fuel flow takes place as above for phase-independent modulation described by opening and closing one (symmetrical Modulation) or two fuel valves, reducing the amount of Fuel supplied through the fuel lines 13, 14 will be varied. Even with the phase-locked Modulation takes place when two fuel valves are used the variation of that supplied through a fuel line Amount of fuel according to the invention regardless of the Modulation of the supplied through the second fuel line Amount of fuel.

Thus, according to the invention, any one can again Phase shift ϕ between the two fuel flows available. According to a preferred embodiment, the Modulation uniform in both fuel lines (ϕ = 0 °). According to a further, particularly preferred embodiment the fuel flows are modulated by 180 ° out of phase, for example at maximum A minimum injection through the fuel line 13 Injection through the fuel line 14.

For the case ϕ = 180 °, the above are shown for the phase-independent modulation was particularly described beneficial effects.

For modulating the injected fuel are preferred Fuel valves are used which are based on control signals a rapid change in the amount of fuel injected react (fast fuel valves).

The amount of fuel injected per unit of time can be in The scope of the present invention varies widely become. As already described above, the invention is carried out a modulation of the amount injected into the premix burner Fuel. According to a preferred embodiment besides the injection of a constant amount of fuel injecting an additional, modulated amount of fuel in the form of a time limited pulse, then then for a specific Time no additional fuel is injected. This The procedure is necessary because with a pulse-like variation of the total fuel flow at certain times none at all Fuel would be injected. However, this would lead to weight loss and extinguish the flame of the burner. Therefore it is done at the same time the injection of a constant amount of fuel and the injection of time-limited pulses of an additional one Amount of fuel.

If one designates the period of the additional fuel injection with t _addition and the period without additional fuel injection with t ₀ , the period of the modulation of the fuel injection results τ = t Encore + t 0 and the frequency too ν = 1 / τ = 1 / (t Encore + t 0 ) .

In the context of the present invention, the term “duty cycle” expresses the ratio of t _addition to τ in percent. With a duty cycle of 50%, the period of additional fuel injection is therefore the period in which no additional fuel is injected. The addition of a constant amount of fuel, i.e. no additional injection, corresponds to a duty cycle of 100%.

Fuel is injected into the premix burner According to the invention with a duty cycle of less than 100%. Prefers the range is 1% ≤ duty cycle ≤ 50%.

Brief description of the drawings

Fig. 1

einen Brenner in perspektivischer Darstellung entsprechend aufgeschnitten;

Fig. 2

den Vormischbrenner gemäß Figur 1, jedoch aus einer anderen Perspektive und in vereinfachter Darstellung;

Fig. 3

ein Flußdiagramm einer Ausführungsform des erfindungsgemäßen Verfahrens zur phasengekoppelten modulierten Eindüsung von Brennstoff;

Fig. 4

eine Auftragung der relativen Druckschwankung bei phasengekoppelter modulierter Eindüsung von Brennstoff (ϕ = 0°) bezogen auf die Druckschwankung bei Eindüsung einer konstanten Brennstoffmenge (100 %) als Funktion der relativen Phase zwischen Meßsignal und momentaner Eindüsung;

Fig. 5

eine Auftragung der relativen Druckschwankung bei phasengekoppelter modulierter Eindüsung von Brennstoff (ϕ = 180°) bezogen auf die Druckschwankung bei Eindüsung einer konstanten Brennstoffmenge (100 %) als Funktion der relativen Phase zwischen Meßsignal und momentaner Eindüsung.

The invention will be explained in more detail below using an exemplary embodiment in conjunction with the drawings. Show it

Fig. 1

a burner correspondingly cut open in perspective;

Fig. 2

the premix burner according to Figure 1, but from a different perspective and in a simplified representation;

Fig. 3

a flowchart of an embodiment of the method according to the invention for phase-coupled modulated injection of fuel;

Fig. 4

a plot of the relative pressure fluctuation with phase-coupled modulated injection of fuel (ϕ = 0 °) based on the pressure fluctuation with injection of a constant amount of fuel (100%) as a function of the relative phase between the measurement signal and the current injection;

Fig. 5

plotting the relative pressure fluctuation with phase-coupled modulated injection of fuel (ϕ = 180 °) based on the pressure fluctuation with injection of a constant amount of fuel (100%) as a function of the relative phase between the measurement signal and the current injection.

Ways of Carrying Out the Invention

According to the most general embodiments described above the present invention, the injection of Fuel independent of the pressure fluctuations in the fuel Combustion system. Alternatively, the injection according to one particularly preferred embodiment so that they with the pressure vibrations are in a fixed phase relationship. This phase-coupled modulated injection of fuel is explained with the aid of a flow chart (FIG. 3). For control the fuel valve 30, 31 becomes a closed one Control loop used. The one measured in the combustion chamber Pressure or luminescence signal becomes noise suppression filtered (reference number 36), phase-shifted (reference number 38), reinforced (reference numeral 40) and for controlling the Fuel valves 30, 31 used. The with the help of Fuel valves 30, 31 modulated fuel is in the Burner 32 injected, to which the chamber 34 connects, the here includes the combustion chamber. In one of the chambers of the Combustion system (calming chamber or combustion chamber) takes place the measurement of the above-mentioned pressure or luminescence signal instead, which closes the control loop.

Figure 4 shows the results of an experimental determination the pressure fluctuations in an embodiment in which the Combustion system at a frequency of around 100 Hz axially symmetric thermoacoustic vibrations tended. In Figure 4 are the pressure fluctuations in phase-coupled modulated injection of fuel based on the Pressure fluctuations with a constant injection Amount of fuel (100%) shown. The fuel injection was done using fast fuel valves from MOOG.

In the present example, a B&K water-cooled microphone the acoustic resonance of the chamber added. The signals were preamplified, bandpass filtered and phase-shifted. The phase shift was there varies systematically between 0 ° and 190 °. The resulting The signal formed the trigger for a signal generator that the Controlled fuel valves via an amplifier stage. The The two fuel flows were modulated without Phase shift to each other (ϕ = 0 °) Figure 4 shows that the Pressure amplitudes with a suitably selected phase shift of up to 87 percentage points are reduced.

Figure 5 shows the results of an experimental determination the pressure fluctuations in an embodiment in which the Combustion system at a frequency of around 100 Hz axially symmetric thermoacoustic vibrations tended. In Figure 5 are the pressure fluctuations with phase-coupled modulated injection of fuel based on the Pressure fluctuations with a constant injection Amount of fuel (100%) shown. The fuel injection was done using fast fuel valves from MOOG.

In the present example, a B&K water-cooled microphone the acoustic resonance of the chamber added. The signals were preamplified, bandpass filtered and phase-shifted. The phase shift was there varies systematically between 0 ° and 360 °. The resulting The signal formed the trigger for a signal generator that the Controlled fuel valves via an amplifier stage. The Signals to the two fuel valves were also in in each case out of phase by 180 ° relative to one another, whereby the modulation of the two fuel flows with one Phase shift of 180 ° (ϕ = 180 °) took place. Figure 5 shows that the pressure amplitudes with a suitably chosen relative phase can be reduced by up to 55 percentage points.

Reference list

1, 2

Partial body

7

Combustion air

13, 14

Fuel lines

15

openings

16

fuel

26

Main central axis

30, 31

Fuel valves

32

burner

34

chamber

36

Filter

38

Phase shifting

40

Reinforce

Claims (16)

Procedure for minimizing the pressure amplitude thermoacoustic vibrations in a combustion system, characterized in that the injection of liquid modulated or gaseous premix fuel. The method of claim 1, wherein the modulation is thereby takes place in addition to a constant amount of Premixed fuel in the form of an additional fuel time-injected pulse is injected, one complete modulation period from the injection of the time-limited pulse and from the following there is no addition of additional fuel. The method of claim 1 or 2, wherein the frequency of the Modulation between 0.3 Hz and 5 kHz, preferably between 5 Hz and 200 Hz. Method according to one of claims 1 to 3, wherein the duty cycle is less than 100%, preferably the condition 1% ≤ duty cycle ≤ 50% is fulfilled. Method according to one of the preceding claims, wherein the current injection of liquid or gaseous Premixed fuel with one in the combustion system measured signal is phase-coupled. The method of claim 5, wherein the in the Combustion system measured signal filtered, is phase-rotated and amplified, and the so obtained Signal fuel nozzles that controls the current injection control of liquid or gaseous premix fuel. The method of claim 5 or 6, wherein the in the Combustion system measured signal or pressure signal is a chemiluminescent signal, preferably a Chemiluminescent signal from the emission of one of the radicals OH or CH. Method according to one of claims 5 to 7, wherein the in signal measured in the combustion system in the combustion chamber or is measured in a calming chamber. Method according to one of the preceding claims, wherein the premix fuel using two Fuel lines (13, 14) is supplied and the Modulation of the amount of fuel supplied by a Fuel valve for both fuel lines. Method according to one of claims 1 to 8, wherein the Premixed fuel using two fuel lines (13, 14) is fed and the modulation of the amount of supplied fuel through one fuel valve each per fuel line. The method of claim 10, wherein modulating the amount of premixed fuel supplied in the two Fuel lines with any relative Phase shift ϕ takes place. The method of claim 11, wherein modulating the amount of premixed fuel supplied in the two Fuel lines with a phase shift ϕ = 0 ° or with a phase shift ϕ = 180 °. Device for controlling thermoacoustic vibrations in a combustion system with a burner, the Burner two fuel lines (13, 14) with openings (15) for injection of liquid or gaseous Has fuel, characterized in that in the Combustion system one or more sensors for measurement thermoacoustic vibrations, and means for control the current injection of premix fuel in Arranged depending on the measurement signal of said sensors are. The apparatus of claim 13, wherein the one or more several sensors arranged in the combustion system for measuring thermoacoustic vibrations pressure sensors, preferably microphones, particularly preferably water-cooled Microphones, are. The apparatus of claim 13, wherein the one or more several sensors arranged in the combustion system for measuring thermoacoustic vibrations optical Sensors for visible or infrared radiation, preferred optical fiber probes. Device according to one of claims 13 to 15, wherein the Means for controlling the current injection of additional fuel means for filtering, phase shifting and amplifying the measurement signal from said sensors.

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